Dimple size is very important! It will directly affect the shot peening strength and coverage. The peening strength is directly proportional to the size of the pits. The coverage rate increases with the size of the pit (when other conditions are the same). Therefore, the size of the pit is very important. The control of the pit size depends on the known (a) size, (b) the influencing factors of the size, and (c) the shot peening method that affects the pit size.

Figure 1 The shape of the pit under low coverage rate

    A typical dimple is shown in Figure 1. The shape is approximately circular. A pit marked at A in the picture is "equivalent to a circle", as in the picture B is a circle with a diameter of d. When the coverage and pit depth are modeled, they can be assumed to be equivalent circles.

    This article is about the factors that affect the size of the pit Perform quantitative analysis. I hope that readers who do not like mathematics will not leave because of the introduction of these necessary equations. Common calculation programs, such as Excel, allow known values ​​to be inserted into these equations. For example, when calculating the pit diameter in Excel, insert the known pellet diameter in A1, the known pit diameter in A2, and the equation in A3: =(A2-(A1^2-A2^2)^0.5 )/2. This equation is the same as equation (1) in the following article.

    Shot size and pit diameter

    The size of the shot material and the size of the pit caused by shot peening exist Linear relationship-other conditions are the same. Both actual observation and theoretical analysis can draw this definite conclusion. Standard shot peening will cause pits, the diameter of which is about 30-50% of the shot. Therefore, we can infer the size range of the pits-because we already know the diameter of the pellets used.

    As shown in Figure 2, when the diameter is In the case of the cast steel shot of D, the range of the estimated pit diameter d. SAE nominal shot size shows that this is the most common size parameter. It can be seen that a huge range of dimple diameters may be encountered. Assuming that d is 40% of D, the diameter of the pit is approximately the same as the SAE value of the shot material in the micron level.

    For example, the diameter of the pits produced by S110 pellets is approximately It is 110 microns, and S460 pellets usually produce pits with a diameter of about 460 microns-1 micron equals 1um.